First, we discuss calculation of scalar triangle
integral \(C_0(s_1,s_2)\)  with two massive external legs.
Here, we follow derivation done in Ref. [1]}.
We start with the integral
\(C_0(s_1,s_2) &=&(i \pi ^2)^{-1} \mu ^{4-D}\, \int d^Dk \, \frac{1}{k^2 (k+l_1)^2 (k+l_2)^2} \,,\) 
